In 1905, Sir William Arbuthnot Lane introduced the use of flat linear steel plates 20 with round screw holes 21 and hole bosses 22, shown in FIG. 1, to surgically repair broken bones. This introduction was motivated by the poor results following cast treatment of many of these fractures. The bone plates must be deformed to conform to the preinjury shape of the bone. Dr. Lane bent and twisted the bone plates with the simple tool shown in FIG. 2. Two of these tools used together permit bending of a bone plate out of the plane of the plate and twisting along the axis of the plate. They are not adequate for bending bone plates in the plane of the plate. Contemporary surgeons use an identical tool to twist the modern bone plates shown in FIGS. 3 and 4, and to bend those plates, but only out of the plane of the plate. Similar tools have long been used by smithies (U.S. Pat. No. 124,362 to Kernon in 1872).
Bend in the plane of the plate is occasionally necessary. For those cases the deliberately weakened plate seen in FIG. 5, known as a reconstruction plate, is used. This plate is often bent with gloved hands or a soft tissue clamp. From time to time such plates bend or break after implantation, causing a loss of fracture fixation. A bender able to bend a strong dynamic compression plate in the plane of the plate would be a great benefit for such cases.
The modern bone plate known as a dynamic compression plate and shown in FIG. 3 includes elongated holes 78 with sloped side walls to compress broken bone ends together. The plates have a transverse curve 9 to improve stiffness, strength and conformity to the bone. Similar bone plates are made in several sizes. Each size is made by several manufacturers. There are subtle differences between manufacturers plates particularly in length and the shape of their longitudinal edge. Modern plates, however, are weakest at the screw holes since the reinforcing bosses 22 around the screw holes 21 of the early bone plate of FIG. 1 have been eliminated in modern plates. Thus, a disproportionate amount of bend takes place at the screw holes regardless of where the bend is desired.
The prior art tool of FIG. 2 has distinct disadvantages when used to bend modern orthopedic bone compression plates. Since a pair of tools are typically used to bend many sizes of plates, the single slot 74 in the bending iron fits the plates poorly. The top jaw 75 is also quite thick to compensate for the weakness of the open slot design. When bending forces are applied, the thick upper jaw and widely abducted handles 76 result in bending forces being applied over an appreciable length of the plate. Additionally, the flat jaw faces crush the transverse curvature of the plates, particularly when used to bend the round holed plates shown in FIG. 4.
Modern plate bending irons 81, shown in FIG. 7, are improved only in that they are scaled for smaller plates. They further suffer from shallow slots so that the sterile plate being bent is prone to pop out and land on the floor if a second operator doesn't hold onto it. Further, the bending irons of FIG. 7 are supplied in pairs where the end slot of one iron is used with the second slot of the second iron, aggravating the tendency to apply force diffusely and bend the plate predominantly where it is weakened by the screw holes.
Prior art does exist addressing the problem of bending elongate metal rods and plates that, for various reasons, has not been of benefit for bending bone plates.
U.S. Pat. No. 2,737,835 to Herz in 1956 discloses a slotted plate bender that principally adds a protractor to measure the bend angle.
U.S. Pat. No. 5,389,099 to Hartmeister in 1995 discloses a slotted round rod bender with an angle near its working end. This is meant to bend a rod already anchored into a patient. The bend helps by increasing the room for the operator's hands on closely approximated tools. The slot axis is, however, perpendicular to the axis of the working end of the tool, requiring some tool end separation. As a result, bending moments are still imprecisely applied over an extended length of the rod. Broad application of bending moment is less of a problem for rods than for bone plates because rods are not weakened by screw holes. The rod bender is slotted and inherently weaker than a pierced bender and hence requires thicker metal at its distal end, further aggravating the imprecise application of bending moments.
U.S. Pat. No. 5,161,404 to Hayes in 1992 discloses a round rod bender with a long angled tip and a hole down the axis of the tip. The bender is well suited to making a single bend of up to 180 degrees in a round rod. However, once a small bend is made the rod will not advance through the bender and neither a diffuse bend nor a second bend can be made. The tool is expensive to made and difficult to clean.
U.S. Pat. No. 3,901,064 to Jacobson in 1975 from the general metalworking art discloses a bender with many parts that immobilizes a malleable strip by clamping it to a base and bending it around a radius pin in the plane of that strip using a long slotted pivoting lever to develop adequate bending moment. The device performs its limited function but it is complex, expensive, and difficult to clean of surgical blood and tissue.
U.S. Pat. No. 5,113,685 to Asher et al. in 1992 discloses a bender for rods and flat plates. A plate bending aperture near the end of the bender is closed at both ends, strengthening it and permitting the aperture to be closer to the end of the bender and somewhat improves the localization of bending moment. The apertures are, however, perpendicular to the plane of the bender and hence do not maximally localize bending moments. The apertures have straight sides with half round ends and hence will flatten the curvature and weaken plates with transverse curves. The apertures are not proportioned for and will not accommodate the very common and useful plates that are made from one third or one half of the circumference of a round tube 30, seen in FIG. 4. The two slots per bender are parallel to and perpendicular to the long axis of the bender. Hence, when stout flat plates are being twisted, the held surfaces of the benders will be adjacent to each other, separated by 90 degrees or separated by 180 degrees. None of these hand positions permits efficient application of arm muscle force to generate a twisting moment.
U.S. Pat. No. 3,866,458 to Wagner in 1975 describes a very complex bender for fixation plates for fractured hips. One half of that bender has long curved jaws that tighten on the curved face of the hip fixation plate. The second half of the bender has a hinged clamp and nipple that mates with a screw fixation hole in the plate. Handles at right angles to the jaws permit bending in one plane only. Half of the bender will only grasp the side plate at a screw hole, roughly every centimeter, not where a bend would best adapt the plate to the shape of the broken hip to be fixed. Once the plate is bent, the long jaws of the second half of the bender will not grasp the plate without deforming the earlier bend. The benders are complex, expensive and bulky. Their broad faces preclude close apposition and well localized bends if bends of more than a few degrees are going to be made.
U.S. Pat. No. 2,800,818 to Larson in 1957 discloses a kit for forming peg board hangers that includes pieces of wire of several diameters, thin straps with a concave-convex transverse cross section and a tool 85 of flat soft steel. The tool includes multiple round 86 and square holes 87 and edge slots 88 for holding round and square wires while they are being bent. More complex, generally C-shaped slots 89 are present at the two ends of tool 85. Each slot has a curved edge which conforms with the convex side of a strap. A central tab 90 having a curved end 91 which conforms with the concave side of the strap is bent upwardly out of the plane of the bar. This design supports the thin transversely curved strap as it is bent through modest angles. The design is inherently unable to cope with stout transversely curved plates and it does little to localize bending moment so that bends will occur where they are desired rather than where the strap is weakened at a screw hole.
An alternative tool known as a plate bending press is shown in FIG. 8 and has enough leverage to bend very stout plates between a curved ram 83 and a curved anvil 82. However, it is even more imprecise than plate bending irons in its application of force and in the curve it imparts to the plate. Furthermore, it requires maintenance and cannot twist the plate.
Accordingly, a need remains for an orthopedic bone plate bender which concentrates force over a short length of the plate, which will support rather than crush the transverse curve of the plate, and which supplies an increased amount of bending force so that a moderate sized operator can bend the most stout bone plates.